1. Field of the Invention
This invention relates to a method of fabricating implantable medical devices such as stents.
2. Description of the State of the Art
This invention relates to radially expandable endoprostheses which are adapted to be implanted in a bodily lumen. An “endoprosthesis” corresponds to an artificial device that is placed inside the body. A “lumen” refers to a cavity of a tubular organ such as a blood vessel. A stent is an example of these endoprostheses. Stents are generally cylindrically-shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other anatomical lumen such as urinary tracts and bile ducts. Stents are often used in the treatment of atherosclerotic stenosis in blood vessels. “Stenosis” refers to a narrowing or constriction of the diameter of a bodily passage or orifice. In such treatments, stents reinforce body vessels and prevent restenosis following angioplasty in the vascular system. “Restenosis” refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty or valvuloplasty) with apparent success.
A treatment involving a stent involves both delivery and deployment of the stent. “Delivery” refers to introducing and transporting the stent through a bodily lumen to a region requiring treatment. “Deployment” corresponds to the expanding of the stent within the lumen at the treatment region. Delivery and deployment of a stent are accomplished by positioning the stent about one end of a catheter, inserting the end of the catheter through the skin into a bodily lumen, advancing the catheter in the bodily lumen to a desired treatment location, expanding the stent at the treatment location, and removing the catheter from the lumen. In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter. The stent is then expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be held in place on the catheter via a retractable sheath. When the stent is in a desired bodily location, the sheath may be withdrawn allowing the stent to self-expand.
Stents have been made of many materials such as metals and plastic, including biodegradable plastic materials. Stents have been formed from wire, tube stock, etc. Stents have also been made from sheets of material which are rolled into a cylindrical shape. The structure of a stent is typically composed of a pattern that allows the stent to be radially expandable. The pattern should be designed to maintain the longitudinal flexibility and radial rigidity required of the stent. Longitudinal flexibility facilitates delivery of the stent and radial rigidity is needed to hold open a bodily lumen.
A number of techniques have been suggested for the fabrication of stents from polymer and metal sheets and tubes. One such technique involves laser cutting or etching a pattern onto a material. Laser cutting may be performed on a sheet of material which is then rolled into a tube. Alternatively, a desired pattern may be formed directly onto a tube. Other techniques involve cutting a desired pattern onto a sheet or a tube via chemical etching or electrical discharge machining Laser cutting of stents has been described in a number of publications including U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005 to Richter, and U.S. Pat. No. 5,906,759 to Richter.
Laser cutting techniques applied to forming patterns for stents have certain shortcomings. For instance, laser cutting a desired pattern onto a tube or sheet can be limited by the kerf width of the laser, the width of a cut made by a laser beam on a material. For example, the kerf width of a laser may make it difficult to cut a desired fine, intricate pattern onto a tube or a sheet. Therefore, methods that address this shortcoming of laser cutting techniques are desirable.